This project entails the mass spectral characterization of the previously uncharacterized products of interactions between the carcinogen benzo(a)pyrene (BP) and DNA in vivo or oligonucleotides in vitro. The in vitro studies were aimed at elucidating the compound(s) comprising so-called "early-eluting" peaks which are observed in the C-18 chromatography of liver DNA digests from tritiated BP- treated A/HeJ mice. The two major techniques used in this work were HPLC and mass spectrometry. Three HPLC systems, employing Partisil 10 SAX, silica or C-18 were developed. Extensive mass spectral studies were done with electron impact or fast atom bombardment. FAB experiments were done in both positive and negative ion modes. The result of this project was that the "early-eluting" material was comprised of tritium- exchanged nucleosides of DNA and RNA, phosphoric acid and tris buffer from the DNA digestion. The in vitro modeling studies examined the chromatographic and mass spectral behavior of unmodified oligonucleotides and those modified in vitro with benzo(a)pyrenediol-epoxide, the ultimate metabolite of BP. The "early-eluting" components identified in the in vivo system were not observed. The mass spectral characterization of the carcinogen modified oligonucleotides is currently in progress.